Apparatus for gas-freeing a fuel tank



Oct.28, 1958 J. w. FORD 58,040-

APPARATUS FOR GAS-FREEING A FUEL TANK Filed March 27, 1956 INVENTOR Jam 3115,;

A ORNEYS United States Patent APPARATUS FOR GAS-FREEING A FUEL TANK John W. Ford, Silver Spring, Md.

Application March 27, 1956, Serial No. 574,342 2 Claims. (Cl. 220-88) (Granted under Title 35, U. 5. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to an apparatus for gas freeing empty fuel storage tanks aboard a ship, and more particularly to an apparatus for carrying out this operation while the ship is under way. The invention further provides a means of gas-freeing tanks by always discharging an inerted gas from the vent, which eliminates the hazard of blanketing the ship with an explosive mixture.

In the operation of fuel carrying tankers it is frequently necessary to render empty tanks free of inflammable vapors, as for example when it is necessary to perform repairs on the tanks and/or change the type of fuel being carried therein. When repairs are to be made on a tank said tank must be rendered free of explosive vapors in order to prevent accidental explosions when welding torches or the like are used in carrying out said repairs and also to prevent repairmen from being subjected to noxious fumes that constitute a health hazard. When changing types of cargo, the tanks must be rendered free of all fumes remaining from a different type of cargo so as to prevent contamination or dilution of a subsequently added different type of cargo. Furthermore it is highly desirable that the fuel tanks be rendered gas free prior to dockage of the vessel in order to save time and expense normally devoted to a gas-freeing operation after the ship has docked.

Economy and having of time are not the only factors involved in this problem. It is pointed out that rules governing gas-freeing of empty tankers have been established by the Coast Guard and the localities in which a ship is docked. The Coast Guard is interested in the safety of the vessel and its crew; while the locality is concerned with the safety of workman and property under its jurisdiction. Certain localities, including Naval establishments, require all tanks to be gas free before docking a vessel regardless of the purpose for which it is docked.

A prior art method of gas-freeing otherwise empty fuel tanks is known as the butterworthing process, such tanks being hereinafter referred to simply as empty tanks. This method consists of directing steam or hot water under pressure from a revolving nozzle against the inner surfaces of an empty tank. One disadvantage of the butterworthing process is that it promotes corrosion, and is otherwise injurious to the plates of the tank. In addition this process introduces water into the tank, which must be removed before reloading; also residual moisture which may remain in the tank enhances corrosion and is detrimental to the cargo. Another major disadvantage is that the process is timeconsuming and delays the ships movement 3 to 4 days longer than the applicants process, since butterworthing can not be carried out until the ship reaches port. Further, the equipment necessary to carry out this process is expensive to install and dismantle.

An object of this invention is to provide an apparatus whereby toxic and/ or inflammable vapors may be evacuated from empty fuel tanks.

A further object is to provide an apparatus whereby toxic and/or inflammable vapors may be removed from an empty fuel tank on a ship while the ship is under way.

Still another object of the invention is to provide apparatus whereby inflammable vapors may be removed IOYil an empty fuel tank on a ship without deactivating the pressure-vacuum relief valve conventionally used in conjunction with such a tank.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawing, wherein the single figure shows an elevational View, partially in section of the gas-freeing apparatus arranged on board a ship 6 in accordance with the invention.

The invention consists of the steps of mixing an inert gas, such as carbon dioxide (CO with the inflammable vapors in an empty tank, and then either automatically or manually releasing the combination of inert gas and inflammable vapors when said combination reaches a non-flammable level, and the apparatus for carrying out said steps.

in order to carry out the above process the ship 6 is provided with an inert gas generator 8. The inert gas is then first conducted, by piping 10, to a gas cleaning device 12, thence by means of a pump 14 to a gas dehumidifier 16, which may be of the type disclosed in applicants patent Ser. No. 2,417,408.

Following dehumidification, the inert gas is conducted through suitable piping 18 into the fuel storage tank iii In order to obtain adequate distribution of the inert gas throughout the interior of the tank 20, gas outlets 22 are provided at both the upper and lower regions of said tank. The flow of gas into the tank is controlled "by suitable means 24, said means being either manually or automatically controlled.

In order to evacuate the combination of inert gas and inflammable vapor from the tank, an exhaust pipeline 26, which communicates with the outside, is provided Within said tank. A plurality of intake openings 28 are provided in said pipe line, said intake openings are located at the bottom of the tank and at the top; since the density of the gas varies, such an arrangement of the openings insures thorough evacuation, or gas-freeing. The pipe line 26 has therein a gas moving blower or ejector 27 adapted to draw the gas out of the tank 2ft. In order to insure that the gas mixture is not discharged to the atmosphere until it has reached a non-flammable state, the pipe line 26 has connected in parallel therewith a seriesv of vapor sensing devices 36 that are adapted to sample the gas in said. line. When a non-inflammable mixture is indicated by the devices 3%, an outlet valve 32 is opened. The vapor-sensing devices 3d are of a conventional type and an example of the same can be seen in the patent to Willenborg, Serial No. 2,049,987.

For automatic control of the valves 32, the vaporsensing devices 36 are connected to their respective valves 32 by any suitable means. That shown is an electric control for the valves 32 through conductors 34 connecting the valves to the vapor-sensing devices 30. In such case the valves are electrically operated. However, an explosion-proof connection should be made because the use of electricity in a tank with explosive vapors could 3 otherwise result in an explosion. Also, instead of electric controls, pneumatic controls can be used in which case the components 34 can be considered a pneumatic interconnection.

-Thus, it can be seen that the gas mixture will T be allowed toescape until it reaches a non-infia able state, at which time theres pective valves 32 wui be opened by the sensing devices 31 and the gas will escape past respective flame arrestors in addition, or as an alternative to the arrangement set forth above, there may be provided r' o a pressure-vacuum relief valve 38 usually uses in con-- junction with fuel tanks. The pressure-vacuum relief valve is used to automatically rei' ve any increase in pressure within the tank Ztl due to a rise in tem erature duringthe day, and to relieve any occur when the temperature drops at m sure-vacuum relief valve 38 is placed in a separate pipeline 40. The pipe-line 40 is used to lead off the combination of vapor and inert gas by placing a bypass line 42 around the pressure-vacuum relief valve A vaporsensing device 3% of the type referred to above, and a valve 32 controlled thereby, are placed in the 32,

thus controlling the passage of the gas around the pressure-vacuum relief valve. In addition, a hand valve 4-4- is placed in the lay-pass line 42 so that the by-pass line i2 may be ciosed.

it is pointed out that while the non-inflammable mixture of gases is being exhausted through pipeline 26 more inert gas is being pumped into the tank by pump 14,

thereby maintaining the mixture Within said tank at a non-inflammable level. By continually pumping inert gas into the tank through lin 18 a continuous outflow of exhaust gas is maintained and at the same time air within the tank is being continuously changed. has been found that after three complete changes or a volume in an empty fuel tank any fumes remaining in said tank, which will of course be mixed with inert gas, are at a nonfiamrnablc level and that therefore no fur-- vapors within an empty tank are rendered non; ambythe instant inventive process and aid ture will remain nonflammabie until thei fuel is placed in said tank.

it should be noted that in accordance with the instant invention no air is drawn into the tank while the inert mixture is being 'e"'hausted, but rathe is drawn in thereby maintaining the vapors in said tank at a nonexplosive revel; the process being carried out until the fumes remaining in the tank, re less of how much air they are mixed with, will remain at a noncxpiosive level.

Under certain circumstances it may be necessary to manually blow-down the tank, without regard to the inflammability of the gas mixture; to provide for this circumstance an additional pipe-line 46 is provided, said pipe-line having only a hand valve iii therein. To use the line 46, the valve 48 is opened and a suitable blower orthe like is turned on, t ereby forcing the gas from the tank through said pipe-line 46.

Thus it can be seen that the structure set forth above provides a safe method "sndufiansroft cila ting inflammable or toxic vapors from a tank by using an inert gas generating and injection system, and providing a number of ways of exhausting the combination of inert gas toXic or inflammable gas vapors from the tank while a ship is still under way; namely, by use of either the pipe line 26 having a gas mover 27 and automatic valves 32 therein, or the by-pass 4-2 aroundthe pressurevacuum relief valve 33, in the lattercasethe pressure c" the ge ire itself being utilized as a gas-moving means, or thirdly by use of the by-pass line '46,'-disregarding the toxic or inflammable nature of the gas being exhausted.

Obv ously many modifications and variations of the n' n are possible in the light of the above to the 'efore to be understood that within the scope or" the appended claims the invention may be practiced otherwise than as specifically described.

' is claimed is:

a ship having a fuel tank and a pressure-vacuum relief vaive connecting said tank with the outside atmosphere, said valve allowing automatic adjustment of pres sure within said tank as the outside temperature rises and falls, the invention comprising means for injecting a quantity of inert gas into said tank, detecting means for d i -ng when the combination ofinflarninable vapors with said tank and said inert gas has reached anonfiannnable state, a by-pass to the outside atmosphere around said pressure-vacuum relief valve comprising a p' Je-line having a valve therein, means operated by said detecting means for automatically opening --said last n ed valve only when the combination of inert gas a inflammable vapors reaches a non-flammable state, thereby allowing the noinflarnmable gas to escape from the tank.

2. Apparatus-for gas-freeing 'an empty fuel-tank of'inmmable vapors contained therein comprising means References Cited in the file of this patent outrun STATES PATENTS Willenborg Aug. 4, 1936 Healy et al Jan. 13, 1953 or continuously injecting a quantity of inert gas into no; tank under pressure greater than atmospheric pres- 

